How do I maximize my speed at the beginning of a round?

Judging from my experience the best strategy, almost guarantied 100% first touch is to hold accelerate and boost before the match starts, then when you're all out of boost do a front flips, they give a bit of boost towards the direction you flip.

Using this strategy I'm almost certain to get first touch should I want it (sometimes I let them push the ball towards me and do a fast counter with a flip).

Although if you are a center spawn, and you have a teammate on either side, don't bother, it's next to impossible to get first touch in that situation.

In my case, I use all the boost (or almost all) but not straight at the beginning, I tend more to use half of the boost, flip and use the rest while in the air right after the flip aiming my car at the ball.

Doing this, you have almost no chances of being thrown after hitting the ball, which gives you advantage if your oponent is. The problem with this tactic is that there's almost no possibility (unless the other player fails) to get a free goal (if 1v1) but there's no chance for him either.